The Object Technology Framework (OTF) includes our continued work on class libraries for manipulating molecular data. The OTF is designed and implemented using an object-oriented paradigm that organizes the functionality into components within a modular and extensible framework. Applications can be created by combining selected prefabricated components with a small amount of custom code, making development of new analysis tools much easier. In particular, we use the OTF in the development of Chimera, our new molecular modeling software.